Trunk sap flow and water consumption of Haloxylon ammodendron growing in the Gurbantunggut Desert

Haloxylon ammodendron distributes widely in the west arid region of China.Studying its water consumption will be beneficial to quantifying ecological water requirement and re-vegetating the desertification region.In the current study,the heat pulse technique was applied to study the trunk sap flow of Haloxylon ammodendron in the Gurbantunggut Desert during the whole growing season.The results showed that the diurnal variation of sap flow of Haloxylon ammodendron was affected multiply by soil moisture,meteorological factors and plant physiological characters.However,the dominant factors that determined the variation of the trunk sap flow of Haloxylon ammodendron were different under different soil water conditions.When the Volumetric Soil Water Content(θv) in the root zone was from 8.7% to 12.1%,the daily trunk sap flow of Haloxylon ammodendron had a very good correlation with soil water content.When the θv in the root zone was more than 12.1%,the diurnal variation of sap flow of Haloxylon ammodendron was mostly affected by meteorological factors.When θv was less than 8.7%,there was mostly affected for the daytime and nighttime sap flow.Under such conditions,there was no correlation between the sap flow and meteorological factors,and it was mostly determined by plant physiological characters.In April,the soil water content in the root zone was the most abundance for the whole year.The curve of the sap flow variability in daytime is a bimodal type and the accumulative process curve is S type.The sap flow during daytime was significantly higher than nighttime.The average diurnal trunk sap flow of Haloxylon ammodendron in April is about two times as much as it in other months.After May,with the soil water content decreases,there are no obvious difference in sap flow between daytime and nighttime,and the accumulative process curve is a linear type.The sap flux of Haloxylon ammodendron varied from 0.156L·cm-2·d-1 for the plant growing in the native Gurbantunggut Desert to 0.876 L·cm-2·d-1 for the plant growing under drip irrigated plantation in the Taklimakan Desert.However,all of the Haloxylon ammodendron plants were in the normal growth conditions,it means that the range of ecological water requirement of Haloxylon ammodendron is very wide.Comparing with other research result,the sap flux of Haloxylon ammodendron growing in the native Gurbantunggut Desert is lowest.The water consumption of Haloxylon ammodendron with trunk diameters of 7.8cm and 9.0cm was respectively 95mm and 117mm from April to September.In addition,the shapes of the diurnal curves of sap flow for Haloxylon ammodendron are similar among plants of different trunk diameters.The bigger diameter size means more water consumption.The low water consumption of Haloxylon ammodendron is very important for the region of desertification with annual mean precipitation at about 150mm,like Junggar Basin.As a result,it is possible to re-vegetate the region without irrigation.With Haloxylon ammodendron as a candidate plant for re-vegetating the region,the contradiction of water demand between the economic development and ecological restoration can be partially solved.